Known in the art is a spark ignition type internal combustion engine which is provided with a variable compression ratio mechanism able to change a mechanical compression ratio and a variable valve timing mechanism able to control a closing timing of an intake valve and which increases the mechanical compression ratio and retards the closing timing of the intake valve as the engine load becomes lower (for example, see Patent Literature 1). In this internal combustion engine, the actual compression ratio is made as high as possible within the range where knocking does not occur and thereby the thermal efficiency is improved.